The first thing I would do is look at the pulse of that injector, you can do it with a LED (not a lamp) if he is receiving the order, that is, the injection pulses, from the ECU, the problem you have there, it is possible that the transistor that sends his pulses sends him hump. I assume that when you changed the injectors of place the problem continues in the 1, if it was not so clear that what is bad is the injector. The other is if it has CNG team, emulators usually work those failures.